Find the inflation index values in previous years.
Retail Price Index (RPI) since 1947. The retail price index calculation was re-based at at value of 100 several times during this period, so the published figures are difficult to track. This calculation adjusts for that and shows how much money you would need to have the equivalent spending power of £100 in 1947.
In 1998 and additional measure, the Consumer Price Index (CPI) was introduced. This provides the CPI based at 100 in 2005, so it tells you how much money you would need in the given year to have the equivalent spending power of £100 in 2005.